1. Field of the Invention
This invention relates to inkjet printheads and, in particular, to sealing nozzle holes in an inkjet printhead to prevent leakage of ink during shipping and storage.
2. Description of Related Art
A plastic tape has been used on inkjet printheads mounted to a print cartridge to seal ink ejection nozzles during shipping and storage of the print cartridge. Sealing the nozzles is intended to stop ink from seeping from the nozzles and clogging the nozzles. Sealing also prevents evaporation of the ink as well as prevents the ink from being contaminated.
FIG. 1 illustrates a prior art inkjet print cartridge 10. Print cartridge body 12 contains liquid ink which is supplied to a substrate (not shown) secured to the back of a nozzle plate 16, which may be formed of metal, plastic, or any other suitable material. The substrate incorporates heater resistors located within ink vaporization chambers. When a heater resistor is energized, a drop of ink is ejected from an associated nozzle 17 formed in nozzle plate 16.
A flexible circuit 18 comprises a polymer tape and has conductive traces (not shown) formed thereon having ends which are bonded to electrodes on the periphery of the substrate surface. The traces are bonded to the electrodes using an automated bonder. Raised epoxy beads 20 are dispensed along the edges of nozzle plate 16 to protect and encapsulate the substrate electrodes and the ends of the traces.
The other ends of the conductive traces terminate in contact pads 22, which contact electrodes of an ink printer when print cartridge 10 is installed in the ink printer.
A flexible plastic nozzle tape 26 is adhesively secured over nozzle plate 16 during storage of print cartridge 10 in an attempt to prevent ink from seeping out of nozzles 17.
FIGS. 2A, 2B, and 2C are taken along line A--A in FIG. 1 and illustrate a drawback of the prior art nozzle tape 26 of FIG. 1.
Nozzle tape 26 in FIG. 2A is positioned over nozzle plate 16 and pressed onto nozzle plate 16 with an applicator 30 (FIG. 2B). A substrate 32 is shown supporting nozzle plate 16.
Tape 26 must seal securely on nozzle plate 16 to prevent leakage of ink from nozzles 17, and the adhesive on tape 26 must be a low-tack adhesive so that the user can easily remove tape 26 from nozzle plate 16 without damaging the printhead or leaving adhesive residue.
Typically, tape 26 is wider than nozzle plate 16 and, therefore, extends over encapsulant beads 20. Adhesion of tape 26 to encapsulant beads 20 is stronger that the adhesion of tape 26 to nozzle plate 16, primarily because the typical tape adhesive used bonds more strongly to epoxy than nozzle plate 16.
Tape 26 commonly has internal tension which may be present when tape 26 is applied to the printhead or may arise because of temperature changes or as the tape shrinks with age. The tension in tape 26 applies a contracting force along the surface of tape 26. The strong bond to beads 20, being above the plane of nozzle plate 16, acts to pull the shrinking tape 26 away from the surface of nozzle plate 16, as shown in FIG. 2C. The lifted tape 26 (FIG. 2C) exposes nozzles 17 and permits leakage of ink 34.
Many attempts have been made to solve the problem of tape lifting. One attempt applies heat and pressure to the tape once the tape is stuck to the nozzle plate. The heat and pressure deform the tape to relieve upward tension in the tape. One problem with deforming the tape is the deformation is not always permanent, and tension is not eliminated. Another problem is the heat and pressure used to deform the tape can damage the nozzle plate or printhead.
A narrow tape, which fits between the beads 20, is successful at preventing tape lifting when the narrow tape is properly aligned with beads 20. However, in volume manufacturing, the close alignment tolerances required by narrow tape are difficult to achieve.
Accordingly, a tape that seals nozzles, does not lift up, and can be inexpensively and accurately applied in volume manufacturing is needed.